Grapefruit, like most citrus fruits and vegetables, have specific growing seasons. They grow only under certain climatic conditions, i.e., tropical and subtropical, such as occur in regions of Florida, Arizona, California, Texas, Brazil, Spain, Italy, Israel and Egypt, and are available in fresh form for only a portion of the year. In order to have grapefruit juice in good quality available year round, the grapefruit juice must be processed for storage and distribution. Since most citrus juices contain about 80 to 90% water, the most economical way to store and distribute the juice is in the form of a concentrate. The bulk of citrus juice commercially processed in the United States since 1950 has been as frozen concentrate.
The difficulty of producing a unique citrus juice concentrate having superior quality can be appreciated when one considers that citrus juice concentrates and other juice concentrates have been available for several decades, and that natural citrus juice products are enjoyed by a large proportion of the general public. Thus, in order to find broad acceptance, a new grapefruit juice concentrate product must overcome the acquired taste preferences of a large segment of the orange juice-consuming public.
In this discussion, references are made to aroma and flavor ingredients present in the juice and juice concentrates. It is known that organoleptic attributes of any commercial beverage are important to consumer acceptance; however, such attributes are uniquely involved in citrus fruit juice acceptability. The term "organoleptic" is defined as "effecting or employing one or more of the organs of special sense", i.e., taste, smell, etc. The challenge of producing a citrus juice product which is acceptable to a broad range of consumers involves making a unique product having acceptable flavor, i.e., taste; distinctive aroma, i.e., smell; acceptable appearance, i.e., sight; and satisfactory mouthfeel, i.e., touch. The aroma and flavor ingredients in any citrus fruit affect each of these organoleptic properties. This is surprising because although there are many ingredients which comprise citrus juice, the aroma and flavor ingredients are present in relatively small amounts.
An important objective achieved by the present invention is that a natural grapefruit juice product is prepared, and a process for its production is provided, which is uniquely different from previously known grapefruit juice products and processes. It is surprising that the grapefruit juice concentrate of this invention, when reconstituted, is close to freshly squeezed grapefruit juice, both in taste and stability. These and other benefits are achieved because the product and processes described herein offer unexpected improvements in virtually all of the organoleptic characteristics mentioned above. These unexpected improvements and advantages are described and illustrated hereinafter.
Most commercial concentration processes use evaporation techniques to remove much of the water from the juice. However, it is widely recognized that evaporation techniques result in the undesirable removal and loss of volatile aroma and flavor compounds along with water, thereby causing a significant deterioration in quality and overall aroma and flavor of the concentrated juice. Because evaporation processes involve heating the juice under conditions which permit oxidation of compounds in the juice, the aroma and flavor compounds in the juice can be chemically altered. For example, lipids can be oxidized, and amino acids and sugars can undergo browning reactions. The degradation products formed can cause off-flavors in the resulting juice concentrates.
Numerous methods have been devised to compensate for the loss of aroma and flavor during evaporation concentration processes. For instance, U.S. Pat. No. 3,140,187, issued to Brent (1964) discloses a method of minimizing the overall loss of aroma and flavor compounds by collecting "essence" of the juice. Essence is the term applied to the first 15% to 20% of the water removed through evaporation, which contains a significant amount of volatile aroma and flavor compounds. The essence is condensed, and the aroma and flavor compounds are recovered and added back to concentrated juice. However, this procedure is not totally satisfactory because only a fraction of the escaping aroma and flavor volatile compounds can be collected and recovered. Thus, there is necessarily a net loss in overall aroma and flavor of the final concentrated product.
Freeze concentration provides an alternative to evaporative concentration. In freeze concentration the objective is to remove water in the form of ice crystals.
U.S. Pat. No. 2,187,572, issued to Meinzer (1940) describes an orange juice concentrate which was prepared by extracting juice, centrifuging the juice to recover a pulp portion and provide a liquid centrifugate, freeze concentrating the centrifugate, and adding back the pulp portion to the concentrated juice. Meinzer suggests that the resulting juice product when reconstituted with water approaches the taste of the starting juice. Specific concentrations of volatile aroma and flavor compounds, and the identification of the key compounds retained within his product are not described.
Schreier et al., Chem. Microbiol. Technol. Lebensm, 6, 78-83 (1979) analyzed the behavior of volatile aroma compounds during freeze concentration of orange juice. During the course of freeze concentration the aroma and flavor compounds were analyzed by gas chromatography and quantitatively determined in the successive juice concentrates as well as in the successively separated ice. Significant amounts of aroma and flavor compounds were found to be removed in separated ice. Average loss of aroma and flavor compounds in the ice during each successive concentration was estimated to be around 12%. It is also evident that a loss of overall quality occurred because a number of oxidation products were formed during this freeze concentration process, such as nootkatone, carvone, geraniol, and alphaterpineol. The formation of these oxidation products and similar compounds can result in a juice product having a notable off-flavor.
Although Schreier employed a freeze concentration process, his analytical data reveal significant losses of volatile compounds. Moreover, because of the open processing used by both Meinzer and Schreier et al., oxidation products were produced. Ideally, freeze concentration removes only pure ice without removing any of the aroma and flavor compounds present in the original juice. If the recovered ice contains occluded aroma and flavor compounds, an inferior quality juice concentrate results.
A generalized procedure for producing a grapefruit juice concentrate involves first extracting the juice from the grapefruit and separating the juice from the rag and seed material. The juice can be separated into a pulp portion and a serum portion. The pulp may be further treated to separate the useful pulp from any small seeds and, if desired, to alter the quantity and size of the pulp. Eventually the pulp is recombined with processed serum.
The serum is concentrated by removing water to produce a concentrated serum. Some serum concentration processes are done in the presence of pulp. Typically, a last step may involve blending the concentrate with a desired amount of pulp to produce a final concentrated product which can be packaged and distributed.
The serum, which remains after pulp, rag, and seed are separated, is known to contain essentially water and the compounds which are responsible for the distinct grapefruit aroma and flavor. As a matter of fact, however, it is probably not possible to categorically assign one specific function to any given ingredient. For instance, a chemical compound which contributes to grapefruit aroma may also contribute to grapefruit flavor.
A grapefruit juice concentrate which can be a pasteurized product and which has substantially 100% of the non-volatile compounds originally present in the serum and at least 65% of the aroma and flavor volatile compounds is very desirable. Moreover, if the concentrate were prepared by a process which did not cause oxidative degradation of the solids in the juice, the resulting concentrate would, when diluted, taste as good as, or better than, the original juice.
It is an object of the present invention to provide a grapefruit juice concentrate having at least 35% solids. The solids comprise pulp, non-volatile compounds and at least 65% of the aroma and flavor volatile compounds which were present in the starting grapefruit juice. It is believed that such a concentrated grapefruit juice product has never been made before this invention. The retained volatile and non-volatile compounds are the very compounds which contribute importantly to the pleasant flavor and aroma of grapefruit juice.
An important contributor to the fruity character of citrus juice aroma and flavor is ethyl butyrate. At least about 0.1%, and preferably at least 0.15% of the aroma and flavor volatile equilibrated headspace compounds measured as gas chromatographic integrator counts, present in the grapefruit juice concentrate of this invention is ethyl butyrate. A second important volatile compound, limonene, is also retained in significant amounts.
It is a further object of this invention to produce a grapefruit juice concentrate which, when reconstituted, tastes as good as and as fresh as freshly squeezed grapefruit juice.
It is still another object of this invention to produce a citrus juice concentrate which can be used as a flavorant in beverages, including carbonated beverages, dry mixes and alcoholic beverages, candies, baked goods, and culinary mixes.
These and other objects of this invention will become apparent by the description of the invention below.
All percentages herein are by weight unless otherwise indicated.